bpo-45126: Ensure sqlite3.Connection is unusable if __init__ fails

Lib/sqlite3/test/test_regression.py

@@ -27,7 +27,7 @@
 import weakref
 import functools
 from test import support
-
+from test.support.os_helper import temp_dir
 from .test_dbapi import managed_connect
 
 class RegressionTests(unittest.TestCase):
@@ -486,6 +486,19 @@ def test_executescript_step_through_select(self):
             con.executescript("select step(t) from t")
             self.assertEqual(steps, values)
 
+    def test_connection_bad_reinit(self):
+        cx = sqlite.connect(":memory:")
+        with cx:
+            cx.execute("create table t(t)")
+        with temp_dir() as db:
+            self.assertRaisesRegex(sqlite.OperationalError,
+                                   "unable to open database file",
+                                   cx.__init__, db)
+            self.assertRaisesRegex(sqlite.ProgrammingError,
+                                   "Base Connection.__init__ not called",
+                                   cx.executemany, "insert into t values(?)",
+                                   ((v,) for v in range(3)))
+
 
 if __name__ == "__main__":
     unittest.main()

Misc/NEWS.d/next/Library/2021-10-22-15-05-10.bpo-45126.roRvx-.rst

@@ -0,0 +1,6 @@
+Prevent segfault if :class:`sqlite3.Connection` reinitialisation fails.
+
+.. warning::
+
+  :class:`sqlite3.Connection` is not adviced, as it may produce undesired
+  side-effects. Creating a new object is preferred to reinitialisation.

Modules/_sqlite/connection.c

@@ -159,6 +159,7 @@ pysqlite_connection_init_impl(pysqlite_Connection *self,
     Py_INCREF(&PyUnicode_Type);
     Py_XSETREF(self->text_factory, (PyObject*)&PyUnicode_Type);
 
+    self->db = NULL;
     Py_BEGIN_ALLOW_THREADS
     rc = sqlite3_open_v2(database, &self->db,
                          SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE |
@@ -167,38 +168,38 @@ pysqlite_connection_init_impl(pysqlite_Connection *self,
 
     if (rc != SQLITE_OK) {
         _pysqlite_seterror(state, self->db);
-        return -1;
+        goto error;
     }
 
     if (!isolation_level) {
         isolation_level = PyUnicode_FromString("");
         if (!isolation_level) {
-            return -1;
+            goto error;
         }
     } else {
         Py_INCREF(isolation_level);
     }
     Py_CLEAR(self->isolation_level);
     if (pysqlite_connection_set_isolation_level(self, isolation_level, NULL) != 0) {
         Py_DECREF(isolation_level);
-        return -1;
+        goto error;
     }
     Py_DECREF(isolation_level);
 
     self->statement_cache = new_statement_cache(self, cached_statements);
     if (self->statement_cache == NULL) {
-        return -1;
+        goto error;
     }
     if (PyErr_Occurred()) {
-        return -1;
+        goto error;
     }
 
     self->created_cursors = 0;
 
     /* Create list of weak references to cursors */
     self->cursors = PyList_New(0);
     if (self->cursors == NULL) {
-        return -1;
+        goto error;
     }
 
     self->detect_types = detect_types;
@@ -222,12 +223,16 @@ pysqlite_connection_init_impl(pysqlite_Connection *self,
     self->NotSupportedError     = state->NotSupportedError;
 
     if (PySys_Audit("sqlite3.connect/handle", "O", self) < 0) {
-        return -1;
+        goto error;
     }
 
     self->initialized = 1;
-
     return 0;
+
+error:
+    self->initialized = 0;
+    self->db = 0;
+    return -1;
 }
 
 static void